This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 11-065046, filed Mar. 11, 1999; and No. 11-068052, filed Mar. 15, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to a dry etching method employed for manufacturing a semiconductor device and, more specifically, to a dry etching method for a stacked film of a metal film containing aluminum as a base metal and metal or a metal compound thin film.
Metal wiring is usually formed on a semiconductor substrate using a dry etching method.
FIG. 1 is a cross-sectional view of a semiconductor substrate on which metal wiring is formed.
As illustrated in FIG. 1, an insulation film 102 is formed on a semiconductor substrate 101. The semiconductor substrate 101 is constituted of a semiconductor such as silicon, while the insulation film 102 is constituted of an insulator such as silicon dioxide (SiO2). The surface of the insulation film 102 is planarized. Metal wiring is formed on the planarized surface of the insulation film 102. The metal wiring is electrically connected to lower wiring (not shown), the semiconductor substrate 101, the gate (not shown) of a MOS transistor, or the like. The metal wiring is also connected to upper metal wiring (not shown) formed on an insulation film 105. The insulation film 105 is constituted of an insulator such as silicon dioxide (SiO2) and formed on the semiconductor substrate 101 so as to coat the metal wiring.
The metal wiring is a stacked film 103 including a metal film 103a and a thin film 103b formed on the metal film 103a. The metal film 103a is constituted of metal including aluminum as a base metal and containing copper and silicon as appropriate. The thin film 103b is constituted of metal for protecting the metal film 103a and improving its reliability as wiring, a metal compound, or a stacked structure of the above metal and metal compound. Titanium and tungsten are selected as the metal, and titanium nitride and tungsten silicide are selected as the metal compound. An example of the stacked structure is shown in FIG. 1.
Conventionally the metal wiring of the stacked film 103 is formed by the steps shown in FIGS. 2A to 2D.
First, as shown in FIG. 2A, a metal film 103a containing aluminum as the base metal, a thin film 103b, and a reflection preventing film 103c are sequentially stacked on the insulation film 102 on the semiconductor substrate 101 to form a stacked film 103xe2x80x2. The reflection preventing film 103c is constituted of materials for preventing light from being reflected toward photoresist, such as an organic compound film containing carbon.
Then, as illustrated in FIG. 2B, photoresist is applied onto the stacked film 103xe2x80x2 to form a photoresist film. Using an exposure technique, a pattern corresponding to the metal wiring is formed on the photoresist film. This photoresist film is developed to form a photoresist pattern 104 having a metal wiring pattern.
As illustrated in FIG. 2C, the stacked film 103xe2x80x2 is subjected to dry etching using the photoresist pattern 104 as a mask. Thus, the stacked film 103xe2x80x2 is formed as a metal wiring pattern.
As shown in FIG. 2D, the photoresist pattern 104 and reflection preventing film 103c are removed. Metal wiring is thus formed of a stacked film 103 of the metal film 103a and thin film 103b. 
After that, as shown in FIG. 1, an insulation film 105 is deposited on the semiconductor substrate 101.
The dry etching of the stacked film 103xe2x80x2 including the reflection protection film 103c, thin film 103b and metal film 103a containing aluminum as the base metal, is performed by a gas system including both chlorine gas (Cl2) and boron trichloride (BCl3). The gas system is usually used for treating an aluminum film. When the stacked film 103 is etched by the gas system containing chlorine gas and boron trichloride, if the flow rate ratio and mixture ratio of the chlorine gas are increased, the thin film 103b is etched vertically as shown in FIG. 3A. However, the metal film 103a is side-etched, and the thin film 103b overhangs the metal film 103a. If the thin film 103b overhangs, a void is likely to be caused between adjacent metal films 103a when the insulation film 105 is deposited, as shown in FIG. 4A.
On the contrary, if the flow rate ratio and mixture ratio of the chlorine gas are decreased, the side-etching of the metal film 103a is reduced as illustrated in FIG. 3B. However, the thin film 103b is not etched vertically but tapered, and its bottom portion is increased in size. If the bottom portion of the thin film 103b is increased in size, the metal film 103a is broadened, and a distance D between adjacent metal films 103a is narrowed as shown in FIG. 4B, with the result that fine metal wiring becomes difficult.
Therefore, a combination of good sides of the above two cases can be considered. The thin film 103b is etched partway by increasing the mixture ratio of the chlorine gas and then the metal film 103a is etched by decreasing it. If the mixture ratio is so changed partway, it is possible to obtain the advantages that the thin film 103b can be etched vertically and the side-etching of the metal film 103a can be prevented.
However, usually, the etching rate of the thin film 103b and metal film 103a is nonuniform within the plane of the semiconductor substrate. Consequently, the above advantages are difficult to obtain uniformly throughout the semiconductor substrate even though the mixture ratio of the chlorine gas is changed partway.
The present invention has been developed in consideration of the above situation and its principal object is to provide a dry etching method capable of patterning a stacked film of a metal film and a thin film, formed on the metal film and including one of metal and a metal compound, in such a manner that the thin film is formed vertically and the metal film is prevented from being side-etched.
To attain the above object, there is provided a method of dry etching comprising: forming a mask layer on a stacked film above a semiconductor substrate, the stacked film including a metal film formed above the semiconductor substrate and containing aluminum as a base component and a thin film formed on the metal film and containing at least one of metal and a metal compound; and patterning the stacked film using the mask layer as a mask for etching, the patterning including: a first step of dry etching the thin film using a first etching gas having a gas composition for preventing the metal film from being processed; and a second step of dry etching the metal film using a second etching gas having a gas composition other than that of the first etching gas.
Another object of the present invention is to provide a dry etching method capable of patterning a stacked film of a barrier layer and a metal film formed on the barrier layer so as to reduce a pattern transfer difference.
To attain the above another object, there is provided a method of dry etching comprising: forming a mask layer on a stacked film above a semiconductor substrate, the stacked film including a barrier layer formed above the semiconductor substrate and a metal film formed on the barrier layer and containing aluminum as a base component; and patterning the stacked film using the mask layer as a mask for etching, the patterning including a step of dry etching the stacked film using an etching gas containing atoms of oxygen.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.